Originally eMMC specifications besides of the physical factors are based on MMC rev 4.2 which is supported by the P2020 eSDHC. The new features introduced in the rev 4.3 to rev 4.5 and rev. 5 of the MMC specs are not supported. I have listened about the P2020 designs with eMMC 4.5. Typically, the eMMC is back compatible to the rev 4.2 MMC specs. To be sure you can ask eMMC producer if its eMMC device is back compatible to the rev 4.2 MMC specs.

We have adopted QorIQ P1021/2010/2020 for our products.And we connected between QorIQ and eMMC for boot device.The eMMC 4.2 device supported by QorIQ is already discontinued.We must change other eMMC device.

eMMC 4.2 added support for SPI mode. (old eMMC support SDR Mode only.)However, since eMMC 4.3, support for SPI mode has been removed again.For this reason, eMMC manufacturers replied that eMMC 5.0 is not back compatible to the rev 4.2 MMC specs.

QorIQ P1021/2010/2020 does not require for the SPI mode at boot time. The P2020 eSDHC does not support the SPI mode at all. The internal ROM SD/MMC driver supports 1-bit operation only (even if the SD/MMC card supports 4 or8-bit parallel access). Of course ROM bootloader can load only small pard of the boot image, i.e. it can load code which reconfigures the eSDHC controller and load the rest.